Pectin polysaccharide contribution to oleosome extraction after wet milling of rapeseed.

Oleosomes are lipid composites providing energy storage in oilseeds. They possess a unique structure, comprised of a triglyceride core stabilized by a phospholipid-protein membrane, and they have shown potential to be used as ingredients in several food applications. Intact oleosomes are extracted by an aqueous process which includes soaking, milling, and gravitational separation. However, the details of the complexes formed between oleosomes, proteins and pectin polysaccharides during this extraction are not known. It was hypothesized that pectins play an important role during the oleosome separation, and different proteins will be complexed on the surface of the oleosomes, depending on the pH of extraction. Rapeseed extracts were treated with and without pectinase (Pectinex Ultra SP-L) and extracted at pH 5.7 or 8.5, as this will affect electrostatic complexation. Acidic conditions led to co-extraction of storage proteins, structured as dense oleosome emulsions, stabilized by a network of proteins and polysaccharides. Pectinase intensified this effect, highlighting pectic polysaccharides' role in bridging interactions among proteins and oleosomes under acidic conditions. The presence of this dense interstitial layer around the oleosomes protected them from coalescence during extraction. Conversely, under alkaline conditions, the extraction process yielded more purified oleosomes characterized by a larger particle size, most likely due to coalescence. Nevertheless, pectinase addition at pH 8.5 mitigated coalescence tendencies. These results contribute to a better understanding of the details of the colloidal complexes formed during extraction and can be used to modulate the composition of the extracted fractions, with significant consequences not only for yields and purity but also for the functional properties of the ingredients produced.

Impact of the Structural Modifications of Potato Protein in the Digestibility Process under Semi-Dynamic Simulated Human Gastrointestinal In Vitro System.

The raising consumer demand for plant-derived proteins has led to an increased production of alternative protein ingredients with varying processing histories. In this study, we used a commercially available potato protein ingredient with a nutritionally valuable amino acid profile and high technological functionality to evaluate if the digestibility of a suspension with the same composition is affected by differences in the structure. Four isocaloric (4% protein, w/w) matrices (suspension, gel, foam and heat-set foam) were prepared and their gastrointestinal fate was followed utilizing a semi-dynamic in vitro digestion model. The microstructure was observed by confocal laser scanning microscopy, protein breakdown was tested by electrophoresis and free amino acids after intestinal digestion was estimated using liquid chromatography/triple-quadruple-mass spectrometry (LC-TQMS). The heat-treated samples showed a higher degree of hydrolysis and lower trypsin inhibitory activity than the non-heat-treated samples. An in vitro digestible indispensable amino acid score was calculated based on experimental data, showing a value of 0.9 based on sulfur amino acids/valine as the limiting amino acids. The heated samples also showed a slower gastric emptying rate. The study highlights the effect of the food matrix on the distribution of the peptides created during various stages of gastric emptying.

Efficient capturing and sensitive detection of hepatitis A virus from solid foods (green onion, strawberry, and mussel) using protamine-coated iron oxide (Fe3O4) magnetic nanoparticles and real-time RT-PCR.

Hepatitis A virus (HAV) continues to be a public health concern and has caused large foodborne outbreaks and economic losses worldwide. Rapid detection of HAV in foods can help to confirm the source of outbreaks in a timely manner and prevent more people getting infected. In order to efficiently detect HAV at low levels of contamination in foods, rapid and easy-to-use techniques are required to separate and concentrate viral particles to a small volume. In the current study, HAV particles were eluted from green onion, strawberry, and mussel using glycine buffer (0.05 M glycine, 0.14 M NaCl, 0.2% (v/v) Tween 20, pH 9.0) and suspended viral particles were captured using protamine-coated magnetic nanoparticles (PMNPs). This process caused a selective concentration of the viral particles, which could be followed by quantitative real-time RT-PCR analysis. Results showed that pH, NaCl concentration, and PMNP amount used for the capturing had significant effects on the recovery efficiency of HAV (P < 0.05). The highest recovery rate was obtained at pH 9.0, 0.14 M NaCl, and 50 µL of PMNPs. The optimized PMNP capturing method enabled the rapid capture and concentration of HAV. A sensitive real-time RT-PCR test was developed with detection limits of 8.3 × 100 PFU/15 g, 8.3 × 101 PFU/50 g, and 8.3 × 100 PFU/5 g of HAV in green onion, strawberry, and mussel, respectively. In conclusion, the PMNP method is rapid and convenient in capturing HAV from complex solid food samples and can generate concentrated HAV sample solutions suitable for high-sensitivity real time RT-PCR detection of the virus.

Protein matrices ensure safe and functional delivery of rosmarinic acid from marjoram (Origanum majorana) extracts.

BACKGROUND: To understand the interactions between carriers and functional ingredients is crucial when designing delivery systems, to maximize bioefficacy and functionality. In this study, two different protein matrices were evaluated as means to protect the extract isolated from marjoram leaves (Origanum majorana), casein micelles from fresh skim milk and soy protein isolate (SPI). RESULTS: Marjoram extract was obtained from pressurization of ethanol and water solvent. Protein dispersions of casein and SPI (5 g L-1 each) with or without marjoram extract (0.1-3 mg mL-1 ) were prepared and homogenized. The physicochemical characterization of charge and entrapment efficiency were conducted. The results demonstrated that entrapment efficiency was highly dependent on the carrier itself where SPI formulations showed 20% higher affinity when compared to casein micelles. To investigate the physiological behaviour of the marjoram-protein dispersions, human macrophages were employed. A non-specific inflammatory response of macrophages stimulated with bacterial lipopolysaccharide was measured for TNF-α, IL-1ß and IL-6 cytokine secretion. CONCLUSION: Casein and SPI protein formulations warranted high bioefficacy of marjoram extract, showing their potential as safe carriers. © 2018 Society of Chemical Industry.

In vitro digestion behavior of water-in-oil-in-water emulsions with gelled oil-water inner phases.

Double emulsions may be able to protect and release in a controlled manner bioactive compounds during digestion of food matrices. It was hypothesized that the physical state and solid content in the inner phases of water-in-oil-in-water (W1/O/W2) emulsions may affect the overall stability and the release behavior of bioactives during in vitro digestion. Therefore, hydrophobic (phytosterols or Vitamin D3) and hydrophilic (Vitamin B12) molecules were incorporated in double emulsions prepared either with a liquid (soybean oil - SO) or oil-fat gel (soybean oil+trimyristin - STO) lipid phase and liquid internal aqueous phase. In addition, the impact of a gelled inner aqueous phase was studied, using high methoxyl pectin. W1/O/W2 emulsions were prepared with polyglycerol polyricinoleate (PGPR) and sodium caseinate as emulsifiers. After the 30min in vitro gastric stage, all double emulsions showed no significant change in size. Lipid crystals were visible in the STO emulsions. Fat crystallization, and the formation of an oil fat gel, led to coalescence of the inner aqueous droplets. The inner aqueous droplets were no longer visible by confocal microscopy after the initial stages of 2h in vitro duodenal digestion. Fat crystals and droplets of non-spherical shape were also noted in the STO double emulsions up to 25min of in vitro duodenal stage. Overall, the STO emulsions had a higher extent of free fatty acid release and consequent bioactive transfer compared to the SO emulsions. The presence of the medium chain fatty acids (from trimyristin), in addition to the surface-to-core distribution of the hydrophobic bioactives within the oil droplet were key factors in lipid digestibility and bioactive release. The STO and SO samples did not differ in terms of the release of the hydrophilic molecule, vitamin B12, over time. On the other hand, there was a significant increase in the stability of the inner water phase, after gastric digestion, when this phase was gelled with high methoxyl pectin. This work demonstrated that the physical properties of the different internal phases of W1/O/W2 influenced lipid digestion and bioactive transfer kinetics during in vitro digestion.

Interfacial dilational properties of tea polyphenols and milk proteins with gut epithelia and the role of mucus in nutrient adsorption.

By interacting with nutrients, the mucus layer covering the intestinal epithelium may mediate absorption. This study aimed to determine possible interactions between epigallocatechin-3-gallate (EGCG), skim milk proteins or their complexes with human intestinal mucin films. The films were extracted from postconfluent monolayers of HT29-MTX, a human intestinal cell line, and a model system was created using drop shape tensiometry. The EGCG uptake tested in vitro on postconfluent Caco-2 cells or co-cultures of Caco-2/HT29-MTX (mucus producing) showed recovery of bioavailable EGCG only for Caco-2 cell monolayers, suggesting an effect of mucus on absorption. Interfacial dilational rheology was employed to characterize the properties of the interface mixed with mucus dispersion. Adsorption of polyphenols greatly enhanced the viscoelastic modulus of the mucus film, showing the presence of interactions between the nutrient molecules and mucus films. On the other hand, in situ digestion of milk proteins using trypsin showed higher surface activities as a result of protein unfolding and competitive adsorption of the hydrolyzed products. There was an increase of viscoelastic modulus over the drop ageing time for the mixed interfaces, indicating the formation of a stiffer interfacial network. These results bring new insights into the role of the mucus layer in nutrient absorption and the interactions of mucus and dairy products.

Complex formation of blueberry (Vaccinium angustifolium) anthocyanins during freeze-drying and its influence on their biological activity.

Biological activity of polyphenols is influenced by their uptake and is highly influenced by their interactions with the food matrix. This study evaluated the complex formation of blueberry polyphenols with fruit matrixes such as pectin and cellulose and their effect on the biological and antiproliferative properties of human colon cell lines HT-29 and CRL 1790. Free or complexed polyphenols were isolated by dialyzing aqueous or methanolic blueberry homogenates. Seven phenolic compounds and thirteen anthocyanins were identified in blueberry extracts. Blueberry extracts showed varying degrees of antioxidant and antiproliferative activities, as well as α-glucosidase activity. Fruit matrix containing cellulose and pectin, or purified polygalacturonic acid and cellulose, did not retain polyphenols and showed very low antioxidant or antiproliferative activities. These findings suggest that interactions between polyphenols and the food matrix may be more complex than a simple association and may play an important role in the bioefficacy of blueberry polyphenols.

Bioefficacy of tea catechins encapsulated in casein micelles tested on a normal mouse cell line (4D/WT) and its cancerous counterpart (D/v-src) before and after in vitro digestion.

Numerous studies have demonstrated that tea catechins form complexes with milk proteins, especially caseins. Much less work has been conducted to understand the metabolic conversions of tea-milk complexes during gastro-duodenal digestion. The objective of this study was to determine the significance of this association on the digestibility of the milk proteins and on the bioaccessibility of the tea polyphenol epigallocatechin gallate (EGCG). An in vitro digestion model mimicking the gastric and duodenal phases of the human gastrointestinal tract was employed to follow the fate of the milk proteins during digestion and determine the bioefficacy of EGCG isolated or encapsulated with the caseins. The samples, before and after digestion, were tested using two parallel colonic epithelial cell lines, a normal line (4D/WT) and its cancerous transformed counterpart (D/v-src). EGCG caused a decrease in proliferation of cancer cells, while in normal cells, neither isolated nor encapsulated EGCG affected cell proliferation, at concentrations <0.15 mg ml(-1). At higher concentrations, both isolated and encapsulated produced similar decreases in proliferation. On the other hand, the bioefficacy on the cancer cell line showed some differences at lower concentrations. The results demonstrated that regardless of the extent of digestion of the nanoencapsulated EGCG, the bioefficacy of EGCG was not diminished, confirming that casein micelles are an appropriate delivery system for polyphenols.

Selenized milk casein in the diet of BALB/c nude mice reduces growth of intramammary MCF-7 tumors.

BACKGROUND: Dietary selenium has the potential to reduce growth of mammary tumors. Increasing the Se content of cows' milk proteins is a potentially effective means to increase Se intake in humans. We investigate the effects of selenized milk protein on human mammary tumor progression in immunodeficient BALB/c nude mice. METHODS: Four isonitrogenous diets with selenium levels of 0.16, 0.51, 0.85 and 1.15 ppm were formulated by mixing low- and high-selenium milk casein isolates with a rodent premix. MCF-7 cells were inoculated into the mammary fat pad of female BALB/c nude mice implanted with slow-release 17 ß-estradiol pellets. Mice with palpable tumors were randomly assigned to one of the four diets for 10 weeks, during which time weekly tumor caliper measurements were conducted. Individual growth curves were fit with the Gompertz equation. Apoptotic cells and Bcl-2, Bax, and Cyclin D1 protein levels in tumors were determined. RESULTS: There was a linear decrease in mean tumor volume at 70 days with increasing Se intake (P < 0.05), where final tumor volume decreased 35% between 0.16 and 1.15 ppm Se. There was a linear decrease in mean predicted tumor volume at 56, 63 and 70 days, and the number of tumors with a final volume above 500 mm3, with increasing Se intake (P < 0.05). This tumor volume effect was associated with a decrease in the proportion of tumors with a maximum growth rate above 0.03 day-1. The predicted maximum volume of tumors (Vmax) and the number of tumors with a large Vmax, were not affected by Se-casein. Final tumor mass, Bcl-2, Bax, and Cyclin D1 protein levels in tumors were not significantly affected by Se-casein. There was a significantly higher number of apoptotic cells in high-Se tumors as compared to low-Se tumors. CONCLUSIONS: Taken together, these results suggest that turnover of cells in the tumor, but not its nutrient supply, were affected by dairy Se. We have shown that 1.1 ppm dietary Se from selenized casein can effectively reduce tumor progression in an MCF-7 xenograft breast cancer model. These results show promise for selenized milk protein as an effective supplement during chemotherapy.

Binding of curcumin to milk proteins increases after static high pressure treatment of skim milk.

Curcumin is a bioactive polyphenolic compound extracted from turmeric with known anti-inflammatory properties, and its hydrophobic nature restricts its solubility and its bioaccessibility. Solubility may be improved upon binding of curcumin to native or treatment-modified casein micelles. The present work demonstrated that high hydrostatic pressure treatment of skim milk increases the binding of curcumin to caseins. The association of curcumin to casein micelles was assessed using fluorescence spectroscopy, either directly or by tryptophan quenching. The amount of curcumin associated with the milk proteins increased in pressure-treated milk, and a further improvement in the amount of bound curcumin was observed upon pressure treatment of a milk/curcumin mixture. However, in this case, some of the curcumin dissociated during storage, contrarily to what was observed for untreated milk. From a molecular standpoint, the data presented here indicate that structural modifications induced by high-pressure treatment and known to affect the structure of milk proteins result in a rearrangement of the amino acid residues in close proximity to the protein-associated curcumin.

Storage stability and physical characteristics of tea-polyphenol-bearing nanoliposomes prepared with milk fat globule membrane phospholipids.

The objective of this work was to better understand the functional properties of milk phospholipids when used as ingredients to prepare liposomes. Liposomal dispersions (10%) were prepared using high-pressure homogenization, and their physical properties as well as their ability to encapsulate tea polyphenols were investigated. The extent of encapsulation, measured by HPLC, increased with tea polyphenol concentration up to about 4 mg·mL(-1). At polyphenol concentrations ≥ 6 mg·mL(-1), the liposome dispersions were no longer stable. The influence of pH (3-7), storage temperature (room temperature or refrigeration), and addition of sugars (0-15%) were studied for liposomes containing 4 mg·mL(-1) polyphenols. The liposomal dispersions were also stable in the presence of peptides. The storage stability of the systems prepared with milk phospholipids was compared to that of liposomes made with soy phospholipids. Soy liposomes were smaller in size than milk phospholipid liposomes, the encapsulation efficiency was higher, and the extent of release of tea polyphenols during storage was lower for milk phospholipid liposomes compared to soy liposomes. The results suggest that milk phospholipids could be employed to prepare tea-polyphenol-bearing liposomes and that the tea catechins may be incorporated in the milk phospholipid bilayer more efficiently than in the case of a soy phospholipid bilayer.

Complexation of high methoxyl pectin with ethanol desolvated whey protein nanoparticles: physico-chemical properties and encapsulation behaviour.

Using a desolvation method, whey protein isolate (WPI) nanoparticles were prepared and mixed with high methoxyl pectin (HMP) solutions (DE 72.8) to form WPI-HMP supramolecular complexes at low pH. Aqueous dispersions containing 5% WPI at pH 9 were desolvated with ethanol, and then diluted in HMP solutions at pH 3. Changes in particle size of the HMP-WPI complexes were studied as a function of HMP concentration. Upon dilution of the WPI nanoparticles in 0.05% HMP at pH 3, the average apparent diameter (d(90)) was around 270 nm, and there were no differences with desolvation level. These nanoparticles would undergo coarsening with storage at room temperature. The complexes showed to withstand homogenization and although heating increased aggregation, the particle size of the heated suspensions improved after homogenization. In addition, the suspensions demonstrated higher interfacial pressures (measured by drop tensiometry) compared to the corresponding unprocessed, desolvated or heated WPI solutions, suggesting their employment as surface active ingredients. The encapsulation efficiency of the desolvated WPI suspensions and desolvated WPI-HMP complex suspensions was studied using a model hydrophilic dye. In all cases, appreciable amounts of dye molecule were encapsulated and retained by the nanoparticles during storage at pH 3.

Interactions of soy protein fractions with high-methoxyl pectin.

A protein-binding technique was employed to visualize, using scanning electron microscopy, the soy protein as well as the association between HMP and soy protein fractions. Image analysis indicated that at pH 7.5 and 3.5 soy protein isolate showed a bimodal distribution of sizes with an average [ d(0.5)] of about 0.05 microm, but at pH 3.8 the proteins formed larger aggregates than at high pH. Addition of HMP at pH 3.8 changed the surface charge of the particles from +20 to -15 mV. A small addition of HMP caused bridging of the pectin between soy protein aggregates and destabilization. With sufficient HMP, the suspensions showed improved stability to precipitation. The microscopy images are the first direct evidence of the interactions between soy proteins with high-methoxyl pectin (HMP).

Comparison on the effect of high-methoxyl pectin or soybean-soluble polysaccharide on the stability of sodium caseinate-stabilized oil/water emulsions.

The interactions of high-methoxyl pectin (HMP) and soybean-soluble polysaccharide (SSPS) with sodium caseinate-stabilized emulsions were investigated using a multitechnique approach, including dynamic light scattering (DLS), electrophoretic mobility measurements, transmission diffusing wave spectroscopy (DWS), and ultrasonic spectroscopy (US). At pH 6.8, both polysaccharides are negatively charged and did not adsorb onto caseinate-coated droplets due to electrostatic repulsion; however, SSPS showed a different behavior compared to HMP in the turbidity parameter 1/l* and sound attenuation parameters measured by DWS and US, respectively. The present study brought the first evidence of the stabilization effect of SSPS in acidified sodium caseinate-emulsions. While destabilization occurred at low polysaccharide concentrations, probably via bridging flocculation, acid-induced aggregation of the oil droplet was completely prevented by 0.2% SSPS or HMP. However, the interaction behavior of SSPS during acidification was different from that of HMP. This was demonstrated by the different development of the parameter 1/l*, droplet sizes, sound attenuation, and velocity.

A diffusing wave spectroscopy study of the dynamics of interactions between high methoxyl pectin and sodium caseinate emulsions during acidification.

A non-invasive technique, diffusing wave spectroscopy (DWS), and traditional dynamic light scattering (DLS) were used to study the interactions of high methoxyl pectin (HMP) with sodium caseinate-stabilized emulsion droplets. At pH 6.8, the droplet size measured by DLS did not change as a function of HMP concentration (up to 0.3%). However, the droplet diameter measured by DWS kept relatively constant up to 0.07% HMP after which it showed drastic increases. The turbidity parameter 1/l* decreased with HMP concentration and levelled off at 0.07% HMP, indicating that the system underwent reorganization and reached equilibrium at 0.07% HMP. During acidification at pH 5.4, right before the pH of aggregation of control emulsions, all emulsions containing 0.05-0.2% HMP showed an increase of 1/l*. This increase indicated the interaction of HMP with sodium caseinate at the interface. Emulsions containing 0.05 and 0.1% HMP also showed destabilization, and the pH of destabilization depended on the concentration of HMP. Sufficient amounts of HMP (0.2%) stabilized the caseinate-coated oil droplets, and the mean square displacement slope was close to 1 throughout, indicating free diffusion of emulsion droplets.

Influence of heating on oil-in-water emulsions prepared with soybean soluble polysaccharide.

The effect of heating on the physicochemical properties of emulsions prepared with soybean soluble polysaccharide (SSPS) was investigated. The emulsions were stable after heating at 90 degrees C for up to 30 min. Heating at different pH values or in the presence of CaCl2 (<10 mM) did not affect the stability; however, at higher concentrations of calcium ions, the emulsion particle size increased. Two fractions, a high molecular weight (HMF) and a low molecular weight (LMF) fraction, were separated from the crude SSPS preparation by gel fitration. Emulsions prepared with SSPS/HMF (MW = 310-420 kDa) showed little change in size with heating, while the protein impurities of the SSPS/LMF fraction formed aggregates by heating at pH 7. Analysis of the heat-induced aggregation of the two fractions of SSPS suggested that the changes in SSPS functionality with heating can be attributed to the protein impurities (LMF) present in the SSPS.

Addition of pectin and soy soluble polysaccharide affects the particle size distribution of casein suspensions prepared from acidified skim milk.

Pectins are negatively charged polysaccharides employed as stabilizers in acidified milk dispersions, where caseins aggregate because of the low pH and serum separation needs to be prevented. The objective of this research was to study the effect of charge on the stabilizing functionality of the polysaccharide in acid milk drinks. Unstandardized pectins with various charges (as degree of esterification, DE) as well as soybean soluble polysaccharide (SSPS) were tested for their stabilizing behavior as a function of pH and concentration. Skim milk was acidified by glucono-delta-lactone and then homogenized in the presence of polysaccharide at different pH values (in the range from 4.2 to 3.0). Measurements of particle size distribution demonstrated that pectins with a DE of 71.4, 68.6, and 67.4 stabilized milk at pH > 4.0. Pectins with a lower DE (63.9%) needed a higher concentration (0.4%) at the same pH to show a monomodal distribution of particle sizes. Pectins with lower DE (<50%) did not stabilize the dispersions. Although this difference in behavior was attributed mainly to the pectin charge, the efficiency in stabilizing the casein dispersion decreased with decreasing pectin size. For example, the high methoxyl pectin (HMP) with 63.9 DE was smaller in size than the HMPs with a higher charge. Pectins showed a pH-dependent stabilization effect, as at pH < 4.0 the dispersions contained aggregates. When SSPS was used to stabilize acid milk, at pH < 4.0, it showed a better stabilization behavior than HMP. When SSPS and pectin were used in combination, the particle size distribution of the acid milk dispersion was pH-dependent, and results were similar to those for samples containing pectin alone. This suggested that in the mixture, pectin dominated the behavior over SSPS, even when an excess of SSPS was added to the dispersions before homogenization.

Stabilizing behavior of soy soluble polysaccharide or high methoxyl pectin in soy protein isolate emulsions at low pH.

The stability of emulsions prepared with soy protein isolates was investigated as a function of pH in the presence of two negatively charged polysaccharides: high methoxyl pectin (HMP) and soy soluble polysaccharide (SSPS). Both polysaccharides are composed of a backbone which contains galacturonic acid but, when added to soy protein isolate-stabilized emulsions, SSPS showed a different behavior than that of HMP. At neutral pH and above a critical concentration of stabilizer (0.05%), HMP caused flocculation of the emulsion droplets via a depletion mechanism. On the other hand, the emulsions containing a similar amount of SSPS did not show creaming or flocculation. At acidic pH (<4.0) the addition of pectin caused extensive droplet aggregation, while no aggregation was observed with the addition of SSPS. The differences in the stabilization behavior between the two polysaccharides can be attributed to their differences in charge, neutral sugars side chains, and molecular weight.

Stabilization of caseinate-covered oil droplets during acidification with high methoxyl pectin.

Polysaccharides are widely used in the food industry to modify the stability of protein-based drinks. However, an in depth knowledge of the interactions occurring in the system is still lacking. In this study, the interactions between sodium caseinate and high methoxyl pectin under acidification conditions were studied nondestructively and without dilution using transmission diffusing wave spectroscopy. Oil-in-water emulsions were prepared with 10% soybean oil and 0.5% sodium caseinate. Various concentrations of pectin (ranging from 0 to 0.2%) were added, and the emulsions were acidified with glucono-delta-lactone. With acidification, a "sol-gel" transition occurred and emulsions containing pectin were more stable at lower pH than those without pectin. Furthermore, the sol-gel transition of the mixtures was more sudden for control emulsions without pectin. While in control samples the final solidlike emulsion after gelation tended to be more inhomogeneous and more dissimilar to the starting emulsion, emulsions with pectin in solution gelled later under acidification. With a sufficient amount of pectin, the emulsions showed no aggregation and the destabilization pH varied depending on the amount of pectin present in the emulsions. At intermediate pH values (pH > 5.5), the emulsions displayed a decrease in particle size, more pronounced in samples containing pectin. The results collected using light scattering in concentrated systems, 10% (v/v) in our case, suggested that pectin stabilizes the emulsion oil droplets forming a network of oil droplets loosely connected by strands of pectin.

Interactions of high methoxyl pectin with whey proteins at oil/water interfaces at acid pH.

The interactions between whey protein isolate (WPI) and high methoxyl pectin (HMP) at pH 3.5 were investigated in situ using ultrasound (US) and diffusing wave spectroscopy (DWS). HMP was added to 10% oil-in-water emulsions containing 1% WPI. At neutral pH, no protein-pectin interactions were observed as both molecules are negatively charged, while at pH 3.5 bridging flocculation occurred via electrostatic interactions. Four different stages were distinguished during the addition of HMP in WPI-stabilized emulsions at pH 3.5. At a concentration below a critical value, no interactions were observed. At concentrations >0.02% HMP, a change in the l factor indicated a change in the ordering of the emulsion droplets, influenced by long-range interactions. At higher concentrations (in the range between 0.04 and 0.06% HMP), attenuation showed significant changes in the surface of the oil droplets, changes which affected the droplet-droplet interactions. At pectin concentrations >0.05%, attenuation of sound and 1/l* decreased, while velocity of sound and particle size increased, as a result of bridging flocculation. These results demonstrated for the first time that methods such as US and DWS combined permit the observation of the early stages of the interactions between two biopolymers at the interface. This is significant in light of increasing efforts in engineering complex interfacial layers.